The present invention relates generally to methods and processes for converting organic materials and organic waste materials into a form that is readily converted into bioenergy.
In recent years, efforts have been devoted to developing energy sources that are alternatives to traditional fossil fuel sources. Some noted problems with fossil fuel are: the potential effects on global warming, the cost of obtaining fossil fuel, and the nonrenewable nature of fossil fuels.
Plants use photosynthesis to store energy from the sun in biomass. A demand exists for cost-effective methods for converting the energy stored in biomass into a form of energy that is readily used by humans. Cellulosic and lignocellulosic biomass is particularly well-suited for energy applications because of its large-scale availability, low cost, and environmentally benign production. For example, conversion of cellulosic and lignocellulosic material into bioenergy may be advantageous, given the rapid growth of algae, switchgrass, other fast-growing grasses, and short rotation woody crops such as shrub willow (Salix spp.) and poplar (Populus spp.) Other examples of lignocellulosic material include, but are not limited to, wood chips, leaves, corn stalks, straw, grass, rice straw, municipal cellulosic waste, animal manure, and human sewage.
Lignocellulose makes up much of the structural matter of plants. Cellulose, hemicellulose, and lignin are the principle components of lignocellulose. Most notably, attempts have been made to convert lignocellulosic material into bioenergy; however, the structure of plant-derived materials presents inherent problems. In a typical lignocellulosic biomass process, raw material feedstock, which is primarily composed of cellulose, is ground up and then pretreated (usually with acid or alkali) to break down the cellulose and separate the three main components of wood (cellulose, hemi-cellulose and lignin). These components are then acted upon by enzymes to form a reactor-ready feedstock, which is a fermentable mixture of glucose and xylose (the basic component of hemi-cellulose). This mixture is then fermented and distilled to create ethanol. However, pretreatment by alkali or acid is accompanied by problems in recovery or disposal of waste alkali or waste acid.
Methods known in the art for pretreating raw material feedstock for use in a reactor, such as an anaerobic digester or a partially-anaerobic digester, include enzymatic treatment; however, enzymatic treatment is relatively slow and costly. Nonetheless, Iogen, Broin, Abengoa and other companies are building plants to process organic material into ethanol. Companies like Diversa, Novozymes, and Dyadic are researching enzymes which can convert cellulose into sugars that can then be fermented to produce ethanol. Andigen uses anaerobic digestion to partially convert biomass into methane; however, the economic viability of conversion of biomass into methane has remained questionable.
An alternative to ethanol production would be to produce methane and/or hydrogen from lignocellulosic material. Currently, anaerobic and partially-anaerobic digesters are useful for converting raw material feedstock into methane and/or hydrogen; however, the yield of methane and/or hydrogen gas from current methods is low and inefficient because most organisms struggle to break down lignin, lignocelluloses, and cellulose, which all have inherent structural stability.
Strong oxidizing agents, such as ozone, have been used to pretreat organic materials. These processes can be used in conjunction with strong acids and bases. However, the use of these methods is relatively costly.
Hence, the need still exists for a simple, cost-effective, and efficient method that could be used by the individual consumer and also be scaled-up for use at waste treatment plants, landfills, and other operations.
The literature is replete with examples of pretreatment protocols; thus, the following pieces of literature are incorporated in by reference. The following U.S. Patents are incorporated by reference: U.S. Pat. Nos. 4,216,054; 4,314,854 4,806,475; 5,023,097; 5,221,357; 5,658,429; 5,865,898; 6,117,324; 6,342,378; 6,500,333; 6,546,740; 6,548,438; 6,555,350; 6,835,560;6,893,565; 7,189,306; 7,297,274; and 7,498,163. U.S. Pat. No. 7,452,467 discloses an example of an anaerobic digester, i.e. the induced blanket reactor, and is incorporated by reference. An induced blanket reactor is one example of a reactor that can be used to convert pretreated organic material into biofuel.
The following U.S. patent applications are incorporated by reference: 2006/0207734; 2007/0259412; 2008/0026431. The following WIPO patent applications are incorporated by reference: WO 2006/032282 and WO 2008/137639. The WO 2008/137639 application (“the '639 application”) and U.S. Pat. No. 7,498,163 (“the '163 patent) both claim methods that include the addition of hydrogen peroxide; however, both claimed processes are non-enabling and would not allow one skilled in the art to practice the invention without undue experimentation. In addition, the concentration of hydrogen peroxide that is used is important. Without the specific parameters that are disclosed herein, undue experimentation would be required before one skilled in the art could determine the optimal concentration of peroxide that is claimed in the present invention.
Removal of the peroxide is an important step. If the peroxide is not removed after pretreatment of the raw material feedstock, use of the reactor-ready feedstock in a reactor, such as an anaerobic digester or a partial-anaerobic digester, will cause extensive foaming because bacterial enzymes will interact with the peroxide to release oxygen (O2); additionally it is believed that peroxides react with organic material to form organic peroxides. These organic peroxides tend to be difficult to destroy and also have the effect of causing excessive foaming. Additionally, if the peroxide is not removed from the reactor-ready feedstock, then the reactor will be contaminated with peroxide which effectively sterilizes the reactor by killing some or all of the bacteria in the reactor.
Washing the reaction sample is one method known in the art to decrease the amount of peroxide that is present in a reaction sample. Washing away the peroxide from a reaction sample usually increases the cost, however, and removes soluble material that is desirable in the feedstock. Lewis et al. discloses experiments where alkaline hydrogen peroxide was used to treat straw. “Effects of Alkaline Hydrogen Peroxide Treatment on In Vitro Degradation of Cellulosic Substrates by Mixed Ruminal Microorganisms and Bacteroides succinogenes S85, Sherry M. Lewis et al. (1988). Some of the treated samples were unwashed, and some were washed thoroughly to remove residual chemicals and then used in fermentation with mixed ruminal microorganisms. Id.
Photolysis is another means for removing peroxide. Some U.S. patents that contain references to photolysis include: U.S. Pat. Nos. 7,488,425 (Method for photolyzing organic matter and method for treating wastewater); 5,762,808 (Destruction of electron affinic contaminants during water treatment using free radical processes); 5,258,124 (Treatment of contaminated waste waters and groundwaters with photolytically generated hydrated electrons); 4,863,608 (Photocatalytic treatment of water for the preparation of ultra pure water); and, 4,008,136 (Process for the treatment of waste water by heterogeneous photosensitized oxidation).
The photolysis of H2O2 by light with wavelengths that are greater than 189 nm in length and less than 249 nm in lengths has been shown to split hydrogen peroxide to produce two hydroxyl radicals; these hydroxyl radicals are reactive oxidizing agents. See Vaghjiani, G. L. and A. R. Ravishankara, 1990, J. Chem. Phys., 92, 996 and Vaghjiani, G. L. A. A., Turnipseed, R. F. Warren, and A. R. Ravishankara, 1192, J. Chem. Phys., 96, 5878.